The present invention relates to a magnetic recording medium and a magnetic recording method for recording in the magnetic recording medium, more specifically, a magnetic recording medium to be used in perpendicular magnetic recording and a magnetic recording method for recording in the magnetic recording medium.
Hard disc devices, which are magnetic recording devices, are widely used in computers, and external storage media, such as various kinds of portable information terminals, e.g., mobile personal computers, game devices, digital cameras, car navigation systems, etc.
Recently, perpendicular magnetic recording media, which can be made more coercive force twice or more in comparison with the conventional longitudinal recording media, is noted. The perpendicular magnetic recording is a magnetic recording mode in which magnetic domains are formed perpendicular to the plane of a recording medium with adjacent recording bits being in antiparallel with each other.
In the perpendicular magnetic recording, the recording is performed by strong recording magnetic field generated from a magnetic head of the single-pole head structure. To this end, below a perpendicular magnetization film which is a magnetic recording layer, a backing layer which functions as an outlet of magnetic fluxes from the single-pole head is formed. Thus, the recording magnetic field generated from the recording head is circulated via the backing layer, and a closed magnetic circuit of the magnetic fluxes is thus formed.
The use of the backing layer makes possible the recording with the stronger head magnetic field and can make the coercive force twice or more in comparison with that of the perpendicular recording media without the backing layer and also with the longitudinal recording media.
The perpendicular magnetic recording media with the backing layer are disclosed in, e.g., Reference 1 (Japanese published unexamined patent application No. 2002-298326), Reference 2 (Japanese published unexamined patent application No. 2003-346315) and Reference 3 (Japanese published unexamined patent application No. 2004-127403). The other related art is disclosed in, e.g., Reference 4 (Japanese published unexamined patent application No. 2001-084658).
The recording layer is formed of a perpendicular magnetization film while the backing layer is formed of a longitudinal magnetization film. The backing layer is thicker than the recording layer. Accordingly, perpendicular magnetic components are often generated in the backing layer due to magnetic interactions, etc. between the recording layer, which is a perpendicular magnetization film, and the backing layer, which is a longitudinal magnetization film. When perpendicular magnetic components are generated in the backing layer, even these components are detected upon the readout, causing medium noises.
For the prevention the interaction between the recording layer and the backing layer, a non-magnetic layer called an intermediate layer is provided between them. However, when the intermediate layer is too thick, the magnetic fluxes from the head cannot arrive at the backing layer, which makes the recording difficult. On the other hand, when the intermediate layer is too thin, the magnetic interaction between the recording layer and the backing layer cannot be sufficiently prevented, and the resultant fluctuations cause medium noises.
When the backing layer has an inversely magnetized domain, forming a 180° magnetic domain wall, leakage fluxes therethrough become spike-shaped noise and multiplexed on readout signals, which often increase the medium noises.
One means which enables high recording density and medium noise reduction is thermal assist recording. The thermal assist recording utilizes changes of the magnetic characteristics of the recording layer due to temperatures. Laser beams are irradiated to heat the recording layer to thereby decrease the coercive force (Hc) of the recording region. However, resultantly, the recording magnetic domains are widened, which restrains the linear density and track density, because the distribution (acuteness) of the recording regions and the recording magnetic fields depends on the light intensity distribution (=heat distribution) of laser beams, and which is also a factor for the medium noises.